The seventh and final “Harry Potter” book comes out a week from Saturday, and the movie version of that book is at least two years away from reaching movie screens. In the meantime, you’ll have to slog your way through the turgid screen version of No. 5, which I award just two stars in today’s Post (screenings start at midnight). The reviews are running 74 percent positive at Rotten Tomatoes, though many of my colleagues seem to be more politely genuflecting to a movie that will rake in serious bucks rather than genuinely enthusiastic. Expect a huge opening — and a big second-weekend drop if J.K. Rowling actually kills off the increasingly tiresome teen wizard in the final book.